1. Field of the Invention
The present invention relates to a method of inspecting the electric characteristics of wafers and an apparatus therefor.
2. Description of the Related Art
A probe apparatus has been used to inspect the electrical characteristics of IC chips formed on a semiconductor wafer (to be referred to as a wafer hereinafter). IC chips which are determined to be defective by the probe apparatus are removed prior to an assembly process so as to realize a decrease in cost or an increase in productivity in the manufacture of semiconductor devices.
The electric characteristics of a wafer are inspected by the probe apparatus in such a manner that a large number of probes attached to a probe card are respectively brought into contact with electrode pads of IC chips formed on the wafer. In this contact state, the electric characteristics of a given IC chip are inspected by a tester connected to the probe card. Subsequently, a mount table on which the wafer is mounted is moved by a predetermined amount to inspect the next IC chip. Such an operation is repeated to automatically perform continuous inspection of the IC chips formed on the wafer. In order to perform such inspection of the electric characteristics of a wafer by a full automatic operation, probe alignment (teaching operation) must be performed to align the distal end position of each probe with a corresponding electrode pad of each IC chip. Consequently, the probe card is replaced, for each type of wafer, with a new one corresponding to each type of wafer. Therefore, probe alignment must be performed upon each replacement.
The probe apparatus comprises an enlarging mechanism, e.g., a microscope, for enlarging the image of a contact portion between a probe and an electrode pad. Probe alignment is performed such that an operator manually performs fine movement of the mount table on which the wafer is mounted while observing each electrode pad and each probe using this microscope. At this time, .theta. alignment of the probe card is also performed.
In the conventional method of inspecting the electric characteristics of wafers, however, an operator manually performs a teaching operation of each probe and each electrode pad in each inspection cycle. For this reason, especially in the manufacture of various types of wafers in small quantities, an operation time for alignment takes a long period of time. In addition, since the number of electrode pads is increased with an increase in integration density of IC chips, alignment becomes more difficult. As a result, the operator requires a longer operation time. For this reason, the operating time of the apparatus is prolonged, and the productivity is lowered. In addition, since alignment is manually performed by an operator, precision varies depending on the skill of each operator, and reliability is impaired. Moreover, if different types of wafers are simultaneously set on the probe apparatus, inspection cannot be continuously performed. Even in different types of wafers, the electrode pads of each IC chip may have the same arrangement. In this case, a single probe card is used. However, since the wafers differ from each other in, e.g., shape, size, or position of IC chips on the wafers, alignment must be performed for each type of wafers. That is, even if the same probe card is used in the manufacture of various type of wafers in small quantities, alignment must be performed every time a type of wafers is changed. Since alignment of wafers needs to be frequently performed in this manner, long-term, continuous automatic inspection cannot be performed, resulting in a decrease in productivity of semiconductor devices.
High-frequency inspection may be performed depending on a type of wafers. In this case, a test head is placed on an upper surface portion of a probe apparatus so as to perform inspection. A microscope is set in an insertion hole formed in the test head. Similarly, in this case, probe alignment is performed in such a manner that an operator manually performs fine movement of a mount table on which a wafer is placed while observing each electrode pad and each probe using a microscope.
A board called a pin electronics board incorporating analog circuits such as a driver and comparator is arranged on a test head to be subjected to high-frequency inspection. Such a test head requires an insertion hole for allowing a microscope to be inserted therein so as to align probes with electrode pads. For this reason, the distance from the wiring of the pin electronics board to each probe is increased to evade the insertion hole. As a result, capacitance and impedance are increased due to the wiring, and hence accurate high-frequency inspection cannot be performed. In addition, if an operator manually performs probe alignment while observing probes and electrode pads through a microscope, probe alignment takes a long period of time. Moreover, precision varies depending on the skill of each operator, and hence reliability is impaired.